In orthopedic surgery, cannulas provide a channel to insert an instrument or device, such as an arthroscope, through them and subsequently into a joint. This is done via a skin incision called a portal. The vast majority of arthroscopic cannulas used in orthopedics are plastic. They generally range in size from 3-10 mm in diameter. A diaphragm at the proximal end prevents any extravasation of fluid.
The surgeon typically controls the arthroscope, or endoscope, in one hand and in an accessory portal can utilize an instrument with the other hand. At times an assistant may control one of the aforementioned as well. Sometimes it is possible to have two accessory portals, which allows the use of two instruments in a joint at the same time that the arthroscope is being used. However, this is dependent on the surgeon, availability of assistants, the type of case (cuff repair, labral repair, ACL reconstruction, etc.), and the size of the joint. It generally requires at least three hands and three portals, and therefore at least two people, and particularly when in close proximity, this can make certain surgeries and procedures difficult.